Sublethal effects of mosquito larvicides on swimming performance of larvivorous fish Melanotaenia duboulayi (Atheriniformes: Melanotaeniidae)

Laboratory studies were conducted to determine the sublethal effects of exposure to selected larvicides on the critical swimming speed (Ucrit) of crimson-spotted rainbowfish, Melanotaenia duboulayi (Castlenau). This native fish is common throughout southeastern Queensland, and it is increasingly being distributed as a biological control agent of mosquitoes. The selected larvicides included, two organophosphate (OP) compounds (temephos and pirimiphos-methyl), two microbial larvicides (Bacillus thuringiensis spp. israelensis Bti] de Barjac and Bacillus sphaericus Bs] Neide), and an insect growth regulator (IGR) (s-methoprene). Exposure to the OP temephos at 10 times the effective field concentration (EFC; 0.33 mg/liter), and OP pirimiphos-methyl at the EFC (0.50 mg/liter), resulted in a significant reduction in the Ucrit of M. duboulayi under controlled conditions. Conversely, exposure to the microbial (Bti and Bs) and IGR (s-methoprene) larvicides at 10 times the EFC had no effect on the Ucrit of M. duboulayi. Accordingly, these products are suitable for integrated pest management programs in Australia.